The invention relates to a warewasher in which the volume of water in the rinse cycle can be controlled so as to provide proper machine operation under conditions of low water pressure.
More particularly, the invention relates to a fresh water rinse machine. This warewasher has a relatively large reservoir located beneath the ware rack which holds about 3 gallons of water. In a typical cycle, the reservoir is filled with water and a proportionate amount of detergent is added for washing. The water in this reservoir is used and reused by pumped recirculation of the wash water for washing successive racks of ware. Fresh water is added after each wash cycle by means of a fresh water spray system which rinses the rack of ware at the proper time in the cycle, after the rack has been washed. Fresh water rinsing is performed while the recirculation pump is off. About 1.2 gallons of fresh water is added to the wash water in each cycle to rinse the current rack of dishes. Because fresh water is added to the tank during the rinse, the system does a partial pumped drain between the wash and rinse cycles. One advantage of this system is that wash water is reused for subsequent cycles. The tank is completely drained only when the water in the tank is fairly soiled.
Conventionally, during the rinse cycle, the control system opens the "fill" valve for a predetermined time. This is commonly referred to as a timed rinse. With nominal water pressure of 20 psi, this rinse adds the required amount of water to the wash chamber. After the end of the timed rinse, the cycle continues for a dwell period.
While it is conventional to use timed rinses to control the volume of water used in the rinse cycle, a number of problems arise during operation of a warewasher in areas having low water pressure or in places where extensive use of water simultaneously will result in such a water demand that water pressure is reduced. A typical water pressure is about 20 psi. Most warewashers should be able to accommodate modest changes of .+-.5 psi in water pressure without affecting the quality of its operation. A low pressure environment therefore, is defined as a situation with less than about 15 psi of water pressure. In such a low pressure environment, the warewasher may not receive a sufficient amount of rinse water. This can deteriorate rinse performance. Less water pressure in the system produces a reduction in water flow, which results in less water added to the machine to rinse the ware. Wash performance also suffers in low water pressure sites using a timed rinse. Proportionately less water is added back to the tank for a subsequent wash cycle. This can result in unacceptable fill levels which offset pump pressure. At low pump pressures, there may be not enough pump pressure to clean some soil off the ware.
One method has been known in the art to adjust for low water pressure. This method employs an adjustable cam timer to control the time of the warewasher's rinse cycle. In a low pressure situation, the cam is manually adjusted to increase the length of time the fill valve is open during the rinse cycle. However, there is no guarantee that the adjusted time will produce the required amount of rinse water.
Therefore, it is an object of the present invention to provide a method for controlling the rinse cycle in a fresh water rinse machine by detecting the volume of water used in the rinse so that in low water pressure areas, the required amount of rinse water will be provided for proper machine operation.